PROJECT SUMMARY: Parasitic Schistosoma blood flukes cause the neglected topical disease schistosomiasis. This disease infects >200 million people but is clinically treated by monotherapy with just one broad spectrum drug, praziquantel (PZQ). The vast scope of the disease and the prospect of PZQ resistance highlight the need for alternative therapies. Indeed, PZQ treatment failure has been reported in the field and resistance can be selected in the lab, indicating that standing genetic variation for resistance already exists. However, drug discovery efforts are hampered by our poor understanding of how existing anti-schistosomal drugs work. Many of these older compounds were discovered >40 years ago using in vivo animal screens. The long-term goal is to identify druggable targets / lead compounds to treat schistosomiasis. The overall objective of this application is to resolve the molecular changes in schistosome biology that underpin the efficacy of existing anti-schistosomal compounds, moving beyond superficial descriptors of worm morphology towards quantitative endpoints that can be assayed for new leads. The central hypothesis is that anthelmintics evoke molecular changes that are more productive screening endpoints than superficial phenotypes. The rationale for this project is that current schistosomiasis drug discovery efforts often focus on in vitro assays for changes in movement or morphology, which are poor predictors of efficacy in vivo. Some anti-schistosomal drugs do cause changes in worm movement / morphology, but others are efficacious in vivo with no effect on movement in vitro, and still other drugs impair movement in vitro but are ineffective in vivo. Better predictors of anti- parasitic action are needed to develop more productive assays. We will pursue two specific aims: (1) Profiling the activity of 10 chemically diverse anti-schistosomal drugs using a panel of molecular assays and (2) Identifying transcriptional signatures of anthelmintics with distinct mechanisms of action. The first aim will resolve mechanistic similarities and differences between these 10 anthelmintics by systematically assessing cellular and molecular changes in worms exposed to drug in vivo. These outcomes will serve as endpoints for the development of quantitative assays for future screens. The second aim will compare the transcriptional responses of parasites to each drug, providing an unbiased readout of global changes to schistosome biology and allowing drugs to be binned according to putative mechanisms of action. Insight into the comparative mechanisms of anti-schistosomal compounds will allow us to rationally select alternative drugs in the event of PZQ treatment failure. This information will also inform drug-combination strategies to prevent the emergence of drug resistance. The research proposed in this application is significant because it will provide new assays for future drug discovery efforts that are better predictors of in vivo anti-parasitic efficacy than existing superficial phenotypes of worm movement and morphology. This research is innovative because it is will establish mechanism-based assays to identify PZQ-alternatives to combat and prevent drug resistance.